1. Field of the Invention
The present invention relates to a heat treatment apparatus for manufacturing a substrate such as a semiconductor wafer, glass, etc., and a method of manufacturing a semiconductor device.
2. Description of the Related Art
As a conventional heat treatment apparatus for thermally treating a substrate, a vertical heat treatment apparatus has been used. The conventional vertical heat treatment apparatus includes a reaction furnace. When a wafer is processed inside the reaction furnace, a predetermined process is performed by heating the wafer to a predetermined temperature under an atmosphere of gases introduced into the sealed reaction furnace.
In this case, the environment (gas purity) of the reaction furnace is critical. In general, the reaction furnace (an inner part of the reaction tube) is controlled so that it can have a negative pressure with respect to the outside (the air) of the reaction furnace. In this case, when a sealing portion (a contacting portion) between the reaction tube and a manifold is leaked, the air flows from the outside to the inside of the reaction furnace. When the air or impurities are mixed into the gas atmosphere in the reaction furnace, it is impossible to perform a desired process, and the processed wafer cannot have desired performance.
Also, when a great quantity of gas temporarily flows into the reaction furnace or a gas exhaust port is closed due to device malfunction, etc., an inner part of the reaction furnace has a positive pressure with respect to the outside of the reaction furnace (atmospheric pressure). In this case, when there is a leak between the reaction tube and the manifold, a processing gas is leaked from the inner part of the reaction furnace to the outside of the reaction furnace. Since the processing gas used in this processing can have risks such as toxicity or explosions, it should not be leaked out of the reaction furnace (the air). That is, a gas should not be leaked from the outside of the reaction furnace to the inner part of the reaction furnace or from the inner part of the reaction furnace to the outside of the reaction furnace.
Accordingly, in order to seal a space between the reaction tube and the manifold as described above, the leakage of the gas from the reaction furnace and the invasion of the external gas from the outside of the reaction furnace are suppressed in the contacting portion by supplying an inert gas to a ring-shaped groove and setting an inner part of the groove to a pressure level (positive pressure) higher than the reaction chamber, for example, the outside of the reaction chamber.
However, since such sealing is incomplete, a large amount of gas may be leaked from the inner part of the reaction furnace, and an external gas may be invaded from the outside of the reaction furnace. Therefore, it is impossible to perform a desired process, or a level of risk may be high.